Certain alkaline earth-nickel phosphates, such as calcium-nickel phosphate or strontium-nickel phosphate are good dehydrogenation catalysts for converting n-butenes to butadiene or for oxydehydrogenating lower aliphatic alkanes and alkenes to dienes. Although they also dehydrogenate alkyl aromatic hydrocarbons to their alkene aromatic derivatives, these catalysts are not as active for this purpose, as are the well-known self-regenerative catalysts containing iron, zinc or magnesium oxides and potassium oxide or a potassium compound convertible to the oxide. Calcium, magnesium or strontium ortho-phosphates, however, are not good catalysts for dehydrogenating either butenes or alkyl aromatic hydrocarbons.
One of the shortcomings of the self-regenerative dehydrogenation catalysts for converting ethylbenzene to styrene is that under acceptable commercially operating conditions the conversion of the ethylbenzene is in the 35-40% range. Selectivity, however, is in the 85-95% range. The self-regenerative catalysts are not sufficiently selective in oxydehydrogenation systems to be useful commercially for converting alkyl benzenes to alkene derivatives in the presence of oxygen.
Therefore, an object of this invention is the provision of a superior catalyst for oxydehydrogenation of an alkyl aromatic compound. Another object is to provide a process for oxydehydrogenating alkyl aromatic compounds in which process superior conversions with high selectivities of the alkyl group to an alkene group are obtained.